Modelizations and Simulations of Nano Devices in nanok calculus

International audienceWe develop a process calculus - the nanok calculus - for modeling, analyzing and predicting the properties of molecular devices. The nanok calculus is equipped with a simple stochastic model, that we use to model and simulate the behavior of a molecular shuttle, a basic nano device currentfly used for building more complex systems

Undecidability of asynchronous session subtyping

Session types are used to describe communication protocols in distributed systems and, as usual in type theories, session subtyping characterizes substitutability of the communicating processes. We investigate the (un)decidability of subtyping for session types in asynchronously communicating systems. We first devise a core undecidable subtyping relation that is obtained by imposing limitations on the structure of types. Then, as a consequence of this initial undecidability result, we show that (differently from what stated or conjectured in the literature) the three notions of asynchronous subtyping defined so far for session types are all undecidable. Namely, we consider the asynchronous session subtyping by Mostrous and Yoshida for binary sessions, the relation by Chen et al. for binary sessions under the assumption that every message emitted is eventually consumed, and the one by Mostrous et al. for multiparty session types. Finally, by showing that two fragments of the core subtyping relation are decidable, we evince that further restrictions on the structure of types make our core subtyping relation decidable.Comment: 36 page

A Sound Algorithm for Asynchronous Session Subtyping and its Implementation

Session types, types for structuring communication between endpoints in distributed systems, are recently being integrated into mainstream programming languages. In practice, a very important notion for dealing with such types is that of subtyping, since it allows for typing larger classes of system, where a program has not precisely the expected behaviour but a similar one. Unfortunately, recent work has shown that subtyping for session types in an asynchronous setting is undecidable. To cope with this negative result, the only approaches we are aware of either restrict the syntax of session types or limit communication (by considering forms of bounded asynchrony). Both approaches are too restrictive in practice, hence we proceed differently by presenting an algorithm for checking subtyping which is sound, but not complete (in some cases it terminates without returning a decisive verdict). The algorithm is based on a tree representation of the coinductive definition of asynchronous subtyping; this tree could be infinite, and the algorithm checks for the presence of finite witnesses of infinite successful subtrees. Furthermore, we provide a tool that implements our algorithm. We use this tool to test our algorithm on many examples that cannot be managed with the previous approaches, and to provide an empirical evaluation of the time and space cost of the algorithm

A Sound Algorithm for Asynchronous Session Subtyping

Session types, types for structuring communication between endpoints in distributed systems, are recently being integrated into mainstream programming languages. In practice, a very important notion for dealing with such types is that of subtyping, since it allows for typing larger classes of system, where a program has not precisely the expected behavior but a similar one. Unfortunately, recent work has shown that subtyping for session types in an asynchronous setting is undecidable. To cope with this negative result, the only approaches we are aware of either restrict the syntax of session types or limit communication (by considering forms of bounded asynchrony). Both approaches are too restrictive in practice, hence we proceed differently by presenting an algorithm for checking subtyping which is sound, but not complete (in some cases it terminates without returning a decisive verdict). The algorithm is based on a tree representation of the coinductive definition of asynchronous subtyping; this tree could be infinite, and the algorithm checks for the presence of finite witnesses of infinite successful subtrees. Furthermore, we provide a tool that implements our algorithm and we apply it to many examples that cannot be managed with the previous approaches

Fertilization Management of Paddy Fields in Piedmont (NW Italy)

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On the boundary between decidability and undecidability of asynchronous session subtyping

Session types are behavioural types for guaranteeing that concurrent programs are free from basic communication errors. Recent work has shown that asynchronous session subtyping is undecidable. However, since session types have become popular in mainstream programming languages in which asynchronous communication is the norm rather than the exception, it is crucial to detect significant decidable subtyping relations. Previous work considered extremely restrictive fragments in which limitations were imposed to the size of communication buffer (at most 1) or to the possibility to express multiple choices (disallowing them completely in one of the compared types). In this work, for the first time, we show decidability of a fragment that does not impose any limitation on communication buffers and allows both the compared types to include multiple choices for either input or output, thus yielding a fragment which is more significant from an applicability viewpoint. In general, we study the boundary between decidability and undecidability by considering several fragments of subtyping. Notably, we show that subtyping remains undecidable even if restricted to not using output covariance and input contravariance

Risk factors and control of hospital acquired infections: a comparison between Wikipedia and scientific literature

Background: nowadays Wikipedia is one of the main on-line sources of general information. It contains several items about nosocomial infections and their prevention, together of items on virtually every scientific topic. This study aims to assess whether Wikipedia can be considered a reliable source for professional updating, concerning Healthcare-associated Infections (HAI). Methods: Wikipedia has been searched in order to gather items on HAI. 387 items were found with a search string. The field of research was reduced at those articles (27 items) containing exhaustive information in relation to prevention of HAI. The messages contained in those articles were than compared with the recommendations of a selected guideline (NICE 2003), completed by a literature search, with the aim of testing their reliability and exhaustivity. Results: 15 Wiki items were found and 51 messages selected. NICE guidelines contained 119 recommendations and 52 more recommendations has been found in a further literature search. 45.1% of Wikipedia’s messages were even found in the guidelines. On this percentage, 21.6% completely agreed with the messages of the guidelines, 15.7% partially agreed, 3.9% disagreed and 3.9% showed different level of evidence in different articles. Moreover, 54.9% of Wikipedia’s messages were not included in the guidelines and 84.2% of the recommendations contained in the guidelines were not present in Wikipedia. Conclusions: Wikipedia should not be considered as a reliable source for professional updating on HAI